Pneumococcal colonization and severity of pneumonia in hospitalized Cambodian children following introduction of the 13-valent pneumococcal conjugate vaccine

OBJECTIVES: This study sought to characterize pneumococcal colonization and clinical/radiological features in Cambodian children admitted to hospital with an illness compatible with pneumonia following national introduction of the 13-valent pneumococcal conjugate vaccine (PCV13). METHODS: Children aged 0–59 months admitted to Angkor Hospital for Children who met the World Health Organization (WHO) case definition for clinical pneumonia were enrolled over a 3-year period. Clinical, radiological and vaccination data were collected at enrolment. A nasopharyngeal swab was collected for detection of pneumococcal colonization using the WHO standard culture method. RESULTS: Between 1 September 2015 and 31August 2018, 2209 analysable illness episodes were enrolled. Pneumococci were detected in 943/2209 (42.7%) children. PCV13 serotypes were detected less frequently in children who had been vaccinated appropriately for their age compared with undervaccinated children: 309/567 (53.6%) vs 216/342 (63.2%) (P=0.006). Age-appropriate PCV13 vaccination was negatively associated with hypoxic presentation [adjusted odds ratio (aOR) 0.72, 95% confidence interval (CI) 0.60–0.87; P=0.0006] and primary endpoint pneumonia on chest x ray (aOR 0.69, 95% CI 0.54–0.90; P=0.006). CONCLUSIONS: The introduction of PCV13 in Cambodia was associated with a decline in vaccine serotype nasopharyngeal colonization, and clinical and radiological severity in children hospitalized with clinical pneumonia.